An example of such control systems for controlling the difference between a value of a current actually flowing in a multiphase rotary machine and a command value for the current such that the difference remains within a preset allowable range is disclosed in Japanese Patent Application Publication No. 2003-235270.
A control system disclosed in the Japanese Patent Application Publication is designed to drive the plurality of switching elements in a non-zero vector mode to thereby bring, to nearly zero, the difference between a value of a current actually flowing through each phase winding of a multiphase rotary machine and a command current value for a corresponding one of the phase windings. After the current difference is brought to nearly zero, the control system is designed to drive the plurality of switching elements in a zero vector mode.
The control system in the zero vector mode works to drive the plurality of switching elements such that line-to-line voltages between the phase windings are all zero. Note that the switching mode for the plurality of switching elements is expressed by voltage vectors. The voltage vectors in which the line-to-line voltages between the phase windings are all zero will be referred to as “zero vectors” hereinafter.
The control system in the non-zero vector mode works to drive the plurality of switching elements such that at least one of the line-to-line voltages between the phase windings are not zero. The voltage vectors in which at least one of the line-to-line voltages between the phase windings are not zero will be referred to as “non-zero vectors” hereinafter.
The configuration of the control system disclosed in the Japanese Patent Application Publication increases durations of the zero vectors to thereby reduce current ripples in the current for each phase winding at the same switching frequency for the plurality of switching elements.